The 7.5-magnitude earthquake that hit Japan’s Noto Peninsula on January 1, 2024, was caused by a unique ‘dual-initiation mechanism’ where energy was released from two separate locations to overcome a fault barrier—an area that typically holds two sides of a fault in place while absorbing the energy from their movement, thus slowing or stopping it.
The beginning of 2024 was marked by significant events, including a magnitude 7.5 earthquake directly under Japan’s Noto Peninsula on New Year’s Day. This disaster resulted in the death of over 280 individuals and the destruction of more than 83,000 homes.
Geologists have discovered that the earthquake initiated nearly at the same time from two points along the fault, which allowed the seismic rupture to encircle and breach a tough area on the fault referred to as a barrier. This unique “dual-initiation” mechanism exerted substantial pressure from both sides of the barrier, resulting in a powerful energy release and considerable shaking throughout the Noto Peninsula.
Prior to the earthquake, there were intense swarms of smaller seismic activity, which can sometimes lead to more significant, catastrophic earthquakes. A research team employed advanced seismic and geodetic technology to carefully investigate the Earth’s movements during these smaller tremors that preceded the larger quake.
Findings of the study, released in the journal Science, shed light on the function of fault barriers, also called asperities, in the formation of earthquakes. This knowledge can enhance the accuracy of seismic risk evaluations and future earthquake predictions.
Earthquakes arise when fractures in the Earth’s crust—known as faults—allow adjacent blocks of rock to shift relative to one another. This shifting is not uniform, as the fault line is irregular, which absorbs energy and ultimately halts movement.
A barrier refers to a rough section that keeps both sides of a fault from moving. Such barriers store the energy from fault movement, which can slow or entirely prevent the shaking. However, a barrier has a limit to the energy it can absorb. Under certain conditions, the accumulated energy can result in a violent rupture, producing strong tremors. While smaller earthquakes may not be sufficient to break a barrier, if there’s a larger movement afterward, the barrier will release all the stored energy.
An international team of researchers led by Lingsen Meng, an associate professor at UCLA, along with UCLA graduate student Liuwei Xu and UC Santa Barbara’s geophysics professor Chen Ji, analyzed geological data and seismic wave recordings. Their goal was to explore the correlation between the swarm of minor earthquakes and the subsequent larger quake, ultimately identifying a previously unidentified barrier in the swarm’s vicinity.
Unexpectedly, the earthquake on New Year’s Day originated almost simultaneously from two different locations along the fault. The energy generated at each site traveled towards the barrier, leading to a catastrophic rupture and severe shaking.
“The earthquake initiated in two spots and propagated together,” Meng explained. “One began waves that moved quickly, triggering another epicenter. Then both segments spread outwards and met in the middle where the barrier was located, thus breaking it.”
This process can be likened to bending a pencil at both ends until it snaps in the center.
The discovery was surprising because, while dual initiation has been seen in simulations, it has been challenging to observe naturally. The conditions necessary for dual-initiation mechanisms can be replicated in laboratories, but they are harder to predict in real-world scenarios.
“We were able to observe it because Japan has excellent seismic monitoring stations and we utilized GPS and satellite radar data comprehensively. We collected as much data as possible! It’s through this data that we achieved a detailed understanding of the fault and could delve into the specifics,” Meng stated.
Most earthquakes lack this level of detailed data, suggesting that earthquakes with dual-initiation mechanisms could occur more frequently than geologists currently realize.
“With enhanced imaging and resolution, it’s likely we’ll identify more instances like this in the future,” Meng mentioned.
Earthquakes originating from dual epicenters are more prone to producing intense shaking due to stronger overall movement. Meng’s team intends to examine future scenarios to ascertain the conditions and likelihood of these types of earthquakes.
“Our findings highlight the intricate nature of how earthquakes start and the essential conditions that lead to major seismic events,” Meng affirmed. “Grasping these processes is crucial for improving our ability to forecast and reduce the consequences of future earthquakes.”
Key takeaways
- A 7.5-magnitude earthquake struck beneath Japan’s Noto Peninsula on January 1, 2024, due to a “dual-initiation mechanism” that released energy from two different areas, breaching a fault barrier that usually absorbs energy and prevents movement.
- An international research team led by UCLA graduate student Liuwei Xu, professor Lingsen Meng, and UC Santa Barbara’s Chen Ji studied a prior seismic swarm and found a previously unknown barrier in that area.
- The research methods utilized by the team could further enhance understanding of the conditions leading to dual-initiation earthquakes in future studies.
